In the field of semiconductor manufacturing, it is common practice to test the semiconductor chips at various stages in the manufacturing process. In particular, due to the time and expense required to package a semiconductor chip, and given the probability that a particular semiconductor chip may have a flaw, it is common practice to inspect the wafers before the wafers are cut up into individual chips. To facilitate this testing, small conductive pads (electrodes) are often located on the surface of the wafer that may be used to connect chip circuitry to an external tester such as a probe device. The probe device may send electrical signals through these electrodes to the circuitry on the wafer. The probe device may also receive electrical response signals from the wafer through these electrodes. These response signals can be processed to determine whether individual chips on the wafer are functioning properly. If a poor electrical connection is made between the probe device and the electrodes, an incorrect status for a chip may be obtained.
With reference to FIG. 1A, a probe device may include a probe card 105 which holds one or more probe needles 100. The probe needles 100 may be oriented in various configurations which are known in the art, such as a vertical paliney probe 120, a vertical P4 C-Probe 121, or a cantilevered probe 122 as shown in FIG. 1B. During testing of a wafer 125 having electrodes 130, probes 100 are brought into contact with electrodes 130 by positioning probe card 105 and wafer 125 relative to each other such that probes 100 contact electrodes 130.
Semiconductor geometry is constantly decreasing. For example, electrodes 130 may be 50 micrometers by 50 micrometers in size and the on-center distance between the pads, otherwise known as the pitch, may be approximately 75 micrometers In order to contact only one electrode at a time, a probe needle of a small diameter is desired. A typical probe needle may have a diameter D shown in FIG. 1C. The probe should be large enough in diameter to provide the mechanical stability and support necessary to keep the probe needle from bending. However, because of the small size of the pads, it is desirable that the end of the probe needle have a smaller diameter with a pointed or needle-like tip 150. Probe needles may be made of many different materials, as is known in the art, and in one embodiment may be made of tungsten. Other materials used for probe tips include nickel alloys, paliney, beryllium copper, tungsten-rhenium, palladium alloys, and other metal coated silicon probes.
With reference to FIG. 1A, electrode 130 of semiconductor device 125 may be formed of aluminum (Al) or other metallic materials known in the art, such as Aluminum-Silicon-Copper pads, Gold pads, and Lead/Tin bumps. An aluminum oxide layer, or other oxide layer, may have formed over the surface of electrode 130 during the wafer manufacturing process. Because aluminum oxide is an insulator, it may be necessary to scratch through the oxide layer so that a reliable contact is formed between the electrode and the probe tip. Scratching through the oxide layer may be accomplished by an overdrive process that includes bringing the semiconductor wafer electrode into contact with the probe tip and moving the wafer and/or the probe card such that the probe needle scrapes and digs into electrode 130.
The overdrive process may break through the oxide layer to make a good electrical connection with the electrode; however, with reference to FIG. 2, extraneous particles such as aluminum, aluminum oxide, silicon, and other types of particles, debris or foreign matter 205 may adhere to the surface of the probe tip. After repeated probing operation, the particles 205 on the probe tip may prevent a good conductive connection from forming with electrode 130 and the probe tip. The repeated probing process may also cause the tip of probe 100 to become blunted 210 as illustrated in FIG. 2. A blunt probe tip may make the probe tip less effective at scratching the surface of the electrode. A blunted probe tip may also cause probe marks to go beyond the specified allowable electrode contact area on the wafer if the blunt end of the tip becomes too large. A pointed probe tip has a smaller tip surface area at the end of the probe tip such that, for the same force, a higher pressure is applied on the aluminum oxide, providing for an enhanced ability to break through the aluminum oxide.
A further problem related to the blunting of a probe tip, is that uneven blunting of probe tips creates probes of different lengths which may cause planarity problems. Probes may wear unevenly because sometimes some of the probes may be probing portions of the wafer where no electrodes exist and the probes touch down on materials of different hardness than the electrode pad. Additionally, probe tips may have burrs that were formed when the probes were made or sharpened, or from adhered debris. Probes may also be uneven in length for other reasons. Regardless of the reason for the variability in the probe tip lengths, planarity problems decrease the ability of the probes to accurately find the target electrode pads. Some efforts to improve planarity involve the blunting of non-blunted probe tips to conform to the length of the already blunted tips. This, however, negatively impacts the performance of the probe cards in other areas as discussed herein.
In response to the problem of particles adhering to the probe needle, a number of techniques have been developed for cleaning probe tips. For example, FIG. 3 is a drawing from U.S. Pat. No. 6,170,116 showing a side view of an abrasive sheet 300 which is composed of a silicon rubber 302 which provides a matrix for abrasive particles 303, such as an artificial diamond powder. In FIG. 3, the probe 100 is inserted into the abrasive sheet 300, and some of the extraneous particles that adhere to the probe tip may be removed or scraped off by the abrasive particles 303. Unfortunately, this process may not remove all of the extraneous particles from the probe tip and may contaminate the probe tip with a viscous silicon rubber film or other particles which adhere to the tip as it is stuck into the silicon rubber matrix. To counteract this secondary particle contamination of the tip, the probe needle may be cleaned by spraying an organic solvent onto the tip of the needle, thereby dissolving and removing some of the viscous silicon rubber film and perhaps some of the secondary particles. Thereafter, the organic solvent may be blown off the probe tip in order to further prepare the tip. This process is time consuming and is performed off-line. Furthermore, the process may result in particles stuck to the tip and even introduce further contaminates.
Other wafer cleaning devices are disclosed such as a cleaning wafer with a mounted abrasive ceramic cleaning block which is rubbed against the probe needles as disclosed in U.S. Pat. No. 6,019,663; the use of a sputtering method to remove particles from the probe tip as disclosed in U.S. Pat. No. 5,998,986; the use of a rubber matrix with abrasive particles and a brush cleaner made of glass fibers as disclosed in U.S. Pat. No. 5,968,282; the employment of lateral vibrational movement against a cleaning surface for removing particles from a probe tip as disclosed in U.S. Pat. No. 5,961,728; spraying or dipping the probe needles in cleaning solution as disclosed in U.S. Pat. No. 5,814,158; and other various cleaning methods such as those disclosed in U.S. Pat. No. 5,778,485 and U.S. Pat. No. 5,652,428.
Many of these methods and devices interrupt the testing of wafers by use of off-line processing to clean the probe tips. Some of these methods introduce further contaminates to the probe tips. Some of these methods exacerbate the blunting of the probe tips. None of these methods address the shaping of probe tips while cleaning on-line.
Therefore, there is a need for an on-line method and apparatus to clean particles from probe tips without the use of solvents or blowing mechanisms. Furthermore, a need exists for a method and apparatus for cleaning probe tips that does not blunt the tip of the probes, but rather enhances the shape of the probe tip. Additionally, there exists a need for the ability to clean and shape the probe tips in a quick and consistent manner with minimal downtime. Furthermore, probe tip shaping extends the life of the probe needle. Probe tip shaping enhances the scratching ability, thereby enhancing the reliability of the electrical contact.